Relationship between Summertime Intraseasonal Oscillations and Submonthly Wave Patterns under Meridional Periodic Fluctuations

In this study, submonthly wave patterns under the periodically fluctuating Japan–South China Sea (JSCS) pattern were separated into intraseasonal oscillation (ISO) westerly and easterly phases. The composite results showed that the wave patterns in the westerly JSCS high and low phases were more effectively organized and situated in a more intense monsoon trough than their counterparts in the easterly phase. Tropical cyclones (TCs) tended to occur over cyclonic systems of the wave patterns where minimal vertical shear axes were also located. More TCs formed in the westerly JSCS phases near areas where maximal moisture convergence was located. Taiwan experienced heavier rainfall during the westerly JSCS phases because the ISO enhanced the monsoon troughs for the cyclonic system of the wave pattern to develop near Taiwan in the westerly JSCS high phase. Additionally, in the westerly JSCS low phase, a stronger southeasterly mean flow generated by the ISO steered the wave pattern and TCs farther west and thus closer to Taiwan. Therefore, the ISO influenced the mean state circulation systems and then steered TCs and the wave patterns to affect Taiwan’s weather.